Introduction
IgG4-related disease is an autoimmune disease of unknown etiology in which IgG4-positive plasma cells infiltrate the body organs and cause swelling, nodules, and hypertrophic lesions in target organs. Approximately 20% and 5% of patients have vision loss and visual field defects, respectively1).
Two major pathological conditions can cause optic neuropathy in this disease: compression or encasement of the optic nerve by an enlarged tissue in the orbit and compression of the optic chiasm by the enlarged pituitary gland. In the former case, compression or encasement of the optic nerve by the enlarged external ophthalmic muscle or localized or diffuse tissue proliferation in the orbit has been reported2). The latter is a condition that can develop in any disease that causes pituitary enlargement, including the present case; however, few studies have reported such cases3)4) and there are no case reports of visual impairment alone.